1. Field of the Invention
The present invention relates to a method and apparatus for controlling a battery car driven by a motor using a battery as a power source, and more particularly to a method and apparatus for controlling a battery car in which regeneration power regenerated by deceleration torque is efficiently recovered, and the energy balance is improved.
2. Description of the Related Art
A battery car has been practically used, which is driven by a motor using a battery as a power source. In the apparatus driven by a battery, regeneration power owing to deceleration torque is stored in the battery to improve the energy balance.
FIG. 1 shows a circuit structure of the conventional apparatus driven by a battery. Referring to FIG. 1, a main circuit unit 1 supplies a variable current to a DC motor 3 from a substantially constant DC power source charged in a capacitor 2 and a battery 6. The polarity and amount of the current are determined by a reference current I.sub.1 input through a current control unit 4 and an input value from a current detection unit 5, based on the extent to which an accelerator pedal or brake pedal is stepped on. The main circuit unit 1, the capacitor 2, and the current control unit 4 constitute a motor control unit 20.
When the apparatus is actuated, a switch 9A is closed by an initial charge control unit 8, with the result that the capacitor 2 is charged by the battery 6 through a reactor 7, the switch 9A, a current limiting resistor 10, and a diode 11. When the capacitor 2 is substantially fully charged, a switch 9B is closed, thereby electrically connecting the battery 6 and the capacitor 2.
When the motor 3 is actuated and motoring is performed, since driving power is supplied from the battery 6 to the motor 3 through the main circuit unit 1, the voltage of the battery 6 is gradually decreased.
When the motor is decelerated while being rotated at a high speed, the voltage of the capacitor 2 is increased to a higher level than that of the battery 6 by regeneration power from the main circuit unit 1. Therefore, charging current flows to the battery 6 through a switch element 12, a diode 13, and the reactor 7. At this time, the charging current is determined by a reference current 13 output from the voltage control unit 14 and limited to or lower than the allowable charging current of the battery 6. When the voltage of the battery 6 reaches a predetermined voltage V.sub.1 presenting full charging states, the voltage control unit 14 set the value of a current 13 to 0, thereby turning off the switch element 12 to stop charging the battery 6. In this state, if regeneration power is generated, the charging voltage of the capacitor 2 is further increased. When the charging voltage of the capacitor 2 reaches a predetermined voltage, a voltage detection unit 16 is operated to output an ON command to a switch element 17, thereby allowing a current to flow through a discharge resistor 18. Thus, the capacitor 2 is prevented from overvoltage.
The conventional apparatus as described cannot efficiently recover the regeneration power for the following reasons: When the battery 6 is fully charged, the voltage of the capacitor 2 is increased and the regeneration power is discharged as heat energy through the discharge resistor 18. Even when the battery is not fully charged, if the motor 3 is decelerated rapidly and a too great regeneration power which exceeds the allowable charging current of the battery 6 is generated in a short period of time, the voltage of the capacitor 2 is increased and the excess regeneration power is discharged as heat energy through the discharge resistor 18.
U.S. Pat. No. 5,053,632 discloses a technique related to the present invention, wherein an engine and a motor are used together.